So what exactly is it that enables movie stars to appear on the silver screen showing off sleek, svelte bodies with no saggy bits while we munch popcorn, grateful for the fact that the darkness hides the slight overhanging paunch?
Of course, celebrities have important advantages over the rest of us. They have the time to follow fitness programmes. They have the money to join exclusive fitness clubs and employ trainers, nutritionists and chefs.
However, according to a man who should know, the fact that celebrities are more likely to be in shape than the rest of us can be put down to something completely different - motivation.
Cornel Chin has trained movie stars including Leonardo DiCaprio, Colin Firth and Audrey Tautou. The one thing they all had in common was that when the cameras started rolling they needed to look good. Kent-based Chin feels that we would all be in better shape if we knew we would be plastered all over the tabloids. "Actors realise they have to be in shape for a film part. The extra motivation that they have over people like you and me I that there is a carrot dangled in front of them. They are told: 'Here's £10 million but you have to be in shape for the part.' Plus they are always in the public eye, so if they are looking just a little bit podgy when they are on the beach with their families they will end up looking silly in the newspapers, and that's hard to deal with."
What you do not need, claims Chin, is a lot of money. And to prove it he has written Celebrity Body on a Budget - a book designed for those who would like to look like Firth or Tautou but do not have their resources. "When I'm working out with my celebrity clients I rarely use a gym. I trained Colin Firth in my own home. With DiCaprio we had a fairly basic gym in Thailand [where he was filming The Beach] and we did a lot of free exercises - you can absolutely get that kind of body on a budget. I normally use dumbbells and stands, a skipping rope, some kick-boxing equipment and a mat - that's it."
In fact, Chin, who is of mixed Carribbean-Chinese, Jewish and Scottish descent, reckons that you can achieve great results without any equipment at all.
The key he says is to incorporate fitness work into your daily routine. "My ethos is that you should try to be generally active - to integrate exercise into your general routine. Imagine if you got off one stop early every single day on your way to work. You would probably burn off 500 calories a week - that's 26,000 calories a year. So take the stairs, not the lift. Walk up the stairs two at a time and you will improve your muscle tone. Walk over to your colleague's desk rather than emailing or phoning, do some squats while you wait for the kettle to boil. Everything adds up. All of these things you can see as a deposit into your fitness bank. And every time you take the lift, you make a withdrawal from the fitness bank."
Chin, who at 46, has an age-defying physique, reckons that having a good body as all about having the know-how. "If you want to build your chest up and the back of your arms and shoulders, there are many different ways to do press-ups. You can have a narrow stance which builds up your triceps or a wide stance which builds different muscles - you need to get the tempo right if you want to build muscle. And if you want a six pack, you can certainly do all the abdominal work without any kind of machine."
So how did Chin's celebrity guinea pigs respond to the challenge of getting fit? "Despite his reputation, Leo DiCaprio is actually quite athletic. He does like a couple of drinks but he is a big fan of basketball and he likes to play dynamic frisbee - he is a very active guy. He didn't enjoy the hard work but I'm not sure that many people would have gone through what he went through. We did two hours every morning and two hours in the evening every single day. He was basically training as if he was a professional athlete. Colin Firth is a lovely guy - and very enthusiastic. We still keep in touch now."
Chin has nothing but praise for his celebrity clients. But he also trains plenty of people who do not have celebrity budgets. It is those who have that celebrity motivation are the ones who tend to succeed. He gives an example: "My oldest client is 95. He lives on the fourth floor and he never gets the lift. Actually he sometimes climbs an additional flight of stairs just for the extra exercise. If a 95-year-old can do that, then anyone can."
‘Celebrity Body on a Budget’ is published by Price World Publishing